/*
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at 
 * 
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *  
 */

using System;
using java = biz.ritter.javapi;
using org.apache.commons.collections;

namespace org.apache.commons.collections.comparators
{

    /**
     * A Comparator that will compare nulls to be either lower or higher than
     * other objects.
     *
     * @since Commons Collections 2.0
     * @version $Revision: 7137 $ $Date: 2011-06-04 21:07:32 +0200 (Sa, 04. Jun 2011) $ 
     *
     * @author Michael A. Smith
     */
    [Serializable]
    public class NullComparator : java.util.Comparator<Object>, java.io.Serializable
    {

        /** Serialization version. */
        private static readonly long serialVersionUID = -5820772575483504339L;

        /**
         *  The comparator to use when comparing two non-<code>null</code> objects.
         **/
        private java.util.Comparator<Object> nonNullComparator;

        /**
         *  Specifies whether a <code>null</code> are compared as higher than
         *  non-<code>null</code> objects.
         **/
        private bool nullsAreHigh;

        //-----------------------------------------------------------------------
        /**
         *  Construct an instance that sorts <code>null</code> higher than any
         *  non-<code>null</code> object it is compared with. When comparing two
         *  non-<code>null</code> objects, the {@link ComparableComparator} is
         *  used.
         **/
        public NullComparator()
            : this(ComparableComparator.getInstance(), true)
        {
        }

        /**
         *  Construct an instance that sorts <code>null</code> higher than any
         *  non-<code>null</code> object it is compared with.  When comparing two
         *  non-<code>null</code> objects, the specified {@link Comparator} is
         *  used.
         *
         *  @param nonNullComparator the comparator to use when comparing two
         *  non-<code>null</code> objects.  This argument cannot be
         *  <code>null</code>
         *
         *  @exception NullPointerException if <code>nonNullComparator</code> is
         *  <code>null</code>
         **/
        public NullComparator(java.util.Comparator<Object> nonNullComparator)
            : this(nonNullComparator, true)
        {
        }

        /**
         *  Construct an instance that sorts <code>null</code> higher or lower than
         *  any non-<code>null</code> object it is compared with.  When comparing
         *  two non-<code>null</code> objects, the {@link ComparableComparator} is
         *  used.
         *
         *  @param nullsAreHigh a <code>true</code> value indicates that
         *  <code>null</code> should be compared as higher than a
         *  non-<code>null</code> object.  A <code>false</code> value indicates
         *  that <code>null</code> should be compared as lower than a
         *  non-<code>null</code> object.
         **/
        public NullComparator(bool nullsAreHigh)
            : this(ComparableComparator.getInstance(), nullsAreHigh)
        {
        }

        /**
         *  Construct an instance that sorts <code>null</code> higher or lower than
         *  any non-<code>null</code> object it is compared with.  When comparing
         *  two non-<code>null</code> objects, the specified {@link Comparator} is
         *  used.
         *
         *  @param nonNullComparator the comparator to use when comparing two
         *  non-<code>null</code> objects. This argument cannot be
         *  <code>null</code>
         *
         *  @param nullsAreHigh a <code>true</code> value indicates that
         *  <code>null</code> should be compared as higher than a
         *  non-<code>null</code> object.  A <code>false</code> value indicates
         *  that <code>null</code> should be compared as lower than a
         *  non-<code>null</code> object.
         *
         *  @exception NullPointerException if <code>nonNullComparator</code> is
         *  <code>null</code>
         **/
        public NullComparator(java.util.Comparator<Object> nonNullComparator, bool nullsAreHigh)
        {
            this.nonNullComparator = nonNullComparator;
            this.nullsAreHigh = nullsAreHigh;

            if (nonNullComparator == null)
            {
                throw new java.lang.NullPointerException("null nonNullComparator");
            }
        }

        //-----------------------------------------------------------------------
        /**
         *  Perform a comparison between two objects.  If both objects are
         *  <code>null</code>, a <code>0</code> value is returned.  If one object
         *  is <code>null</code> and the other is not, the result is determined on
         *  whether the Comparator was constructed to have nulls as higher or lower
         *  than other objects.  If neither object is <code>null</code>, an
         *  underlying comparator specified in the constructor (or the default) is
         *  used to compare the non-<code>null</code> objects.
         *
         *  @param o1  the first object to compare
         *  @param o2  the object to compare it to.
         *  @return <code>-1</code> if <code>o1</code> is "lower" than (less than,
         *  before, etc.) <code>o2</code>; <code>1</code> if <code>o1</code> is
         *  "higher" than (greater than, after, etc.) <code>o2</code>; or
         *  <code>0</code> if <code>o1</code> and <code>o2</code> are equal.
         **/
        public int compare(Object o1, Object o2)
        {
            if (o1 == o2) { return 0; }
            if (o1 == null) { return (this.nullsAreHigh ? 1 : -1); }
            if (o2 == null) { return (this.nullsAreHigh ? -1 : 1); }
            return this.nonNullComparator.compare(o1, o2);
        }

        //-----------------------------------------------------------------------
        /**
         *  Implement a hash code for this comparator that is consistent with
         *  {@link #equals(Object)}.
         *
         *  @return a hash code for this comparator.
         **/
        public int hashCode()
        {
            return (nullsAreHigh ? -1 : 1) * nonNullComparator.GetHashCode();
        }

        /**
         *  Determines whether the specified object represents a comparator that is
         *  equal to this comparator.
         *
         *  @param obj  the object to compare this comparator with.
         *
         *  @return <code>true</code> if the specified object is a NullComparator
         *  with equivalent <code>null</code> comparison behavior
         *  (i.e. <code>null</code> high or low) and with equivalent underlying
         *  non-<code>null</code> object comparators.
         **/
        public bool equals(Object obj)
        {
            if (obj == null) { return false; }
            if (obj == this) { return true; }
            if (!obj.GetType().equals(this.GetType())) { return false; }

            NullComparator other = (NullComparator)obj;

            return ((this.nullsAreHigh == other.nullsAreHigh) &&
                    (this.nonNullComparator.equals(other.nonNullComparator)));
        }

    }
}